Vibration-proof rubber has been widely used in various fields in which the vibration-proof rubber is interposed between two members constituting a vibration transmission system to establish vibration-proof connection between the two members, and, for example, in the automobile field, the vibration-proof rubber has been used as an engine mount, a body mount, a member mount, a suspension bush, and the like.
As a vibration-proof rubber composition used for the vibration-proof rubber, in general, a composition containing diene rubber, silica small particles, and a silane coupling agent has been used (Japanese Unexamined Patent Application Publication No. 11-255964). However, kneading of the silica small particles and the silane coupling agent with rubber increases the viscosity in an unvulcanized state due to re-aggregation of silica, thereby degrading compression set and storage stability.
Therefore, in order to improve this degradation, pre-treated silica prepared by surface-treating silica with a silane coupling agent has recently been used. Examples proposed as a rubber composition using the pre-treated silica include a rubber composition for an engine mount containing at least one type of diene rubber as a main rubber component and silica fine particles which are previously surface-treated with a silane coupling agent and which have a BET specific surface area of 40 to 170 m2/g (Japanese Unexamined Patent Application Publication No. 11-193338), a rubber composition containing 100 parts by weight of a rubber component containing at least one type of diene rubber, 20 to 120 parts by weight of silica pre-treated with 2 to 15% by weight of a silane coupling agent, and 2 to 10% by weight of alkoxysilane of silica before being pre-treated (Japanese Unexamined Patent Application Publication No. 2002-3652), and the like.